I have a rattling sound under acceleration that starts at about 15-20 mph and last for just a couple of seconds. It may be there longer but because of wind and engine noise I can't hear it any more. It sounds almost exactly like engine knocking/pinging, but it's not. I know that because if I rev the engine in neutral, it doesn't make any weird noises, no matter how hard, snappy, or fast I rev it. Is it possible that this is coming from the transmission? I wouldn't be surprised if it was something rubbing, but I got underneath the car and removed anything the exhaust could be rubbing against and went for a drive and the noise was still there. Any ideas? Those who had transmission failures...did you have any such warnings? Thanks.